In manufacturing lines of semiconductor substrates and thin film substrates, optical inspection apparatuses that inspect a minute defect present on a surface of a sample have been widely used to obtain a high yield of products (for example, see PTLS 1 and 2). Generally, an optical inspection apparatus radiates light condensed at a width of several-ten μm to the surface of the sample, condenses/detects light (hereinafter, referred to as the target light) transmitted, scattered, or reflected from a defect, and performs defect detection. An apparatus that is put to practical use at the present time can inspect a defect of several-ten nm or more.